Spacecraft use docking systems to dock one space vehicle with another. Space vehicles include satellites, space shuttles, nano-satellites, free-flying satellites and similar other space objects. For purposes of this disclosure, the international space station may also be considered a space vehicle.
Docking systems typically include a docking device having reflective sensors (also referred to as “docking targets”) for generating a visual output. Cameras for machine vision systems monitor the visual output and provide location data for navigation control of space vehicles. Navigation control of space vehicles depends on the accuracy of the collected data.
Space vehicle docking systems typically use sensor computers (like autonomous rendezvous and docking (ARD) sensor) for interpreting visual output and process information for navigational computers. Navigational computers analyze information received from the sensor computer, process the information and provide navigational data to flight computers. Flight computers provide thrusters with information for controlling the position and attitude of the space vehicle in three dimensional spaces.
Docking cameras of machine vision systems work in visible or infrared light. Therefore, it is a desirable for docking devices to work in infrared and visible wavelengths.
Docking devices known in the prior art have docking targets with vertical projections and flat spots. Flat spots provide only two dimensional data while the vertical projections enable docking cameras to measure a three dimensional angle unambiguously. These vertical projections move with respect to the flat spots when viewed from different angles. A two dimensional projection is formed which helps define the position and relative orientation of the vehicle.
FIG. 1A shows a conventional docking target 100 having flat spots (102) and a vertical projection (104). Vertical projection 104 may be round (FIG. 1A) or they may be rectangular 104′ (FIG. 1B).
These vertical projections are fragile and inconvenient. Any mistake in maneuvering of a space vehicle may damage the protrusions. Replacement of docking targets would be expensive and inconvenient.
Lenticular targets and holograms (shown as 100A) that are flat may also be used as docking targets. However, lenticular targets and holograms are wavelength sensitive and work only in visible wavelengths and do not operate in infrared wavelengths. Optics used in lenticular targets and holograms glint under harsh space lighting and do not transmit infrared wavelength. Furthermore, holograms, including white light holograms, require controlled lighting at specific angles, which is generally not the case in space docking as sunlight is very harsh and is at random angles. Therefore, lenticular targets and holograms are not effective as docking targets in space vehicles.
Therefore, there is a need for a docking device that has flat docking targets, is not constrained by visible light or infrared light and which can provide three dimensional data for safe and effective docking.